1. Field of the Invention
The invention is a continuation-in-part of U.S. patent application Ser. No. 07/940,849 filed Sep. 4, 1992, and pertains to an efficient method for producing levoglucosan as pure, white crystals, and more particularly, an efficient method for isolating levoglucosan in a highly pure crystalline form by treating pyrolysis oil derived from waste newsprint. The waste newsprint is reduced to fine particle size and subsequently treated with a hot mineral acid, after which the newsprint is filtered off, and dried to a solid paper material. Thereafter, the dried paper material is pyrolyzed to produce pyrolysis oils. The pyrolysis oils are subjected to liquid-liquid extraction with methyl isobutyl ketone (MIBK) to remove heavy tar materials and to provide an aqueous fraction of oils primarily containing levoglucosan. The aqueous fraction is then treated with excess calcium hydroxide and freeze-dried to produce a dry solid residue, whereupon the dry solid residue is extracted with ethyl acetate to provide levoglucosan.
2. Description of the Prior Art
In efforts to manufacture conventional wood adhesives from renewable resources, instead of petrochemicals, methods have been investigated for converting levoglucosan into components of fast-curing work adhesives.
Unfortunately, however, as presently available, pure levoglucosan is very expensive. Further, presently known processes for providing levoglucosan give levoglucosan in a form that is contaminated by impurities, such that levoglucosan is not inexpensively and simply provided as a white crystalline material of high yield and high purity when using these processes.
A cellulose-derived pyrolysis oil from which levoglucosan is derived is subjected to an extraction with chloroform to remove colored impurities in U.S. Pat. No. 3,235,541; however, the process of this patent entails a pretreatment of the cellulose-derived pyrolysis oil and is encumbered by the fact that chloroform is highly toxic. After the chloroform extraction, the aqueous solution is concentrated to a syrup that is dissolved in acetone, and levoglucosan is isolated as a pure crystalline compound from the acetone solution after filtration and recrystallization.
Starch containing feedstocks are utilized to provide levoglucosan from pyrolysis oils by treating the starch containing feedstocks with chemicals such as sulfur dioxide, calcium chloride and calcium acetate in U.S. Pat. No. 3,478,012; however, the process of this patent necessitates pretreatment of the feedstocks before pyrolysis.
U.S. Pat. No. 3,309,356 is directed to a process for separating levoglucosan and carbohydrate acids; however, this patent pertains to the isolation of levoglucosan from pyrolysis oils that contain phenolics (i.e. wood as feedstock). Organic solvents are used to extract the phenolics from the crude pyrolysis oils, then the extracted aqueous solution is dried azeotropically with methyl isobutyl ketone and the resulting organic solution is filtered to obtain levoglucosan from the filtrate. No data on the purity of the levoglucosan are provided.
A process for separating levoglucosan and carbohydrate derived acids from aqueous mixtures is described in U.S. Pat. No. 3,374,222. In this process, after the pre-extraction of phenolics, the aqueous solution is treated with basic metal salts, to precipitate polymeric carbohydrate-derived acids that are present in the pyrolysis oil. The precipitated materials are then removed through filtration to obtain a filtrate of an aqueous solution from which levoglucosan is isolated after elution through a cation exchange column.
There is a need extant in the art of producing levoglucosan to develop an efficient method for providing a high yield of pure, crystalline levoglucosan from waste newsprint as from well as cellulose; however, pyrolysis oils from lignocellulosic materials such as newsprint are more complex than those obtained from cellulose, in that the oils from newsprint also contain phenolics, furans, and other colored materials, which make the isolation of levoglucosan more difficult.